This invention relates generally to food processing machines, such as a mixer-grinder, and more particularly to a meat grinder which incorporates a bone chip remover.
Generally, meat grinders employed in the processing of beef, pork, veal or lamb are used to form a ground meat product from utility grade meat. Utility grade beef, for example, generally includes older animals, such as older cows or steers, or parts of the younger steers that cannot be used for the better cuts of beef. Generally, the choice cuts of animals raised for beef are not processed in the mixer-grinders to which the present invention applies.
The meat cutters in large meat processing or meat packing plants are commonly paid in accordance with their production in removing the meat from the bones of slaughtered animals. As a result of the preparation of the meat, a certain amount of foreign material, most commonly gristle and bone particles or chips, finds its way into the meat product applied to a grinder. Where workers may be working at a piece rate, they may not be quite as careful in cutting the meat from the carcass and from the bones, and if they nick the bone with a knife, that piece of bone may ultimately finds its way into the grinder. For example, circular hand-held knives are used to remove meat from ribs, and if the cutter is not particularly careful, some bone may be removed along with the meat from the ribs and may find its way into a grinder. It has been estimated that, in larger meat processing houses grinding utility grade beef, approximately 1/10th of one percent (0.1%) of the meat product applied to grinders may consist of bone or bone chips.
Large mixer-grinder machines capable of handling several hundred pounds a minute or more, are generally operated on a substantially continuous basis. Quite often, the meat is subject to a double grind with the first grind being applied to a plate having 1/2 (12.1 mm) or 3/8 inch (9.53 mm) openings therethrough to form a relatively coarse grind. Then this meat product is either immediately ground a second time in a second grinder to a final cut with holes about 1/8 of an inch (3 mm) diameter, or the meat product is applied to a mixer-grinder where it is mixed and blended with seasoning, fat, extenders or the like, and then ground at a final grinding plate having the smaller diameter holes. Thus, the burden falls upon the grinder having the finer or final plate to prevent the unwanted bone particles from getting into the final product.
Not only is it undesirable to permit the bone particles to go through a grinder and ultimately into the final ground meat product, the presence of such particles, or excessive gristle, or other product which does not readily pass through the grinder plate severely degrades the productivity and capacity of the grinder. After a relatively short period of operation the capacity is reduced to the point where cleaning becomes necessary. Also, permitting the same to remain in the region of the grinder plate for any substantial period of time increases the likelihood that some of the bone chips will be reduced in size and passed through the plate, thus lowering the grade or quality of the ground meat. Thus, it is a customary practice in high capacity grinders, to stop the grinding operation after about twenty to thirty minutes of operation and clean out the collected bone chips, gristle and the like from the region behind the plate and about the knife. For example, a second grind at a grinder may initially produce approximately 280 lbs/min of ground meat product, but this will drop in about one-half hour's time to 230 or 240 lbs/min, depending upon the sharpness and quality of the cutting knife, the grinding plate, and the amount of fat, bone or gristle in the product. It becomes necessary to remove the grinding plate and clean out the bone chips and other particles. Running the grinder for a longer period of time increases the likelihood of cutting and grinding up the bones and passing them through the plate into the final product. Skilled laborers can thus clean out a grinding head in about five minutes down time, representing a loss of about ten minutes per hour or about a 15 percent loss of productivity.
There have been a number of attempts to produce a bone chip remover for a meat grinder, or to incorporate bone chip removing apparatus into existing grinder constructions. A primary problem in designing such systems is caused by the difficulty of separating the bone chips and other undesirable components such as gristle, from the meat itself without suffering a substantial loss of valuable meat product. Thus, it has proved to be difficult to separate the entrained chips, which account for only a very small percentage of the total meat product, in an effective manner.
Collection of bone chips, cartilage, gristle, sinews and fat in meat grinders tends to occur in large measure in the central region around the hub of the knife, immediately behind the plate. Whether this is the result of the much larger area at the outer periphery of the plate being open for the flow of meat therethrough or the likely greater force exerted by the outer flights of the grinder worm is not known. However, this congregation at the center of the plate has caused a number of parties seeking solutions to the problem of bone chip removal to capture them centrally and cause them to exit centrally through a tube or pipe to a disposal location outside of the grinder. Exemplary of such efforts are Seydelmann, U.S. Pat. No. 3,847,360 issued Nov. 12, 1974 and Seydelmann, U.S. Pat. No. 3,934,827 issued Jan. 27, 1976. Several commercial versions of central discharge of bone chips presently exist in the U. S. marketplace. Such units rely primarily on high meat pressure within the grindr, rather than physical action of mechanical parts, to force collected bone chips along its disposal path.
Another effort at removing bone chips in meat from behind the final grinding plate and causing their disposal is shown in U.S. Pat. No. 4,153,208 of Vomhof et al, issued May 8, 1979. In that structure, a unique knife arrangement is provided to take advantage of the central pressure packing of bone chips, channel the bone chips (and presumably red meat also) through grooves provided internally of the knife blades themselves, use the internal pressure of meat to drive the chips toward an outer peripheral region, and then use combined frictional force and pressure to drive the bone chips from the cylinder through a tangential slot after they have once been captured in a peripheral region. Like the aforementioned Seydelmann patents, Vomhof also accepts the apparent natural tendency of waste to congregate around the knife hub. Unfortunately, expensive meat can also easily follow the same path as the waste product, in both types of units where centralized collection is relied upon.
In yet another form of bone chip removal illustrated in Jensen, U.S. Pat. No. 4,204,647 of May 27, 1980, an attempt is made to counter the inward packing force of bone chips and gristle with knife blades which are intended to physically drive such particles radially outward toward the periphery of the cylinder. The cylinder periphery is provided with a series of slots in the knife plane, into which bone chips and the like are packed. As shown in this patent, a hinged shackle is clamped about the cylinder exterior to cover the slots. The machine must be stopped when the bone chips are to be removed, the shackle removed, and the machine jogged to cause meat pressure to extrude the bone chips or whatever is contained in the slots therefrom. The outer surface of the cylinder is then scraped clean and the shackle reinstalled. In a commercial version of this latter device, a slotted ring is provided in place of the shackle. The ring may be actuated by an air cylinder from one position in which the slots in the ring are out of alignment with the cylinder slots to close the slots, to a second position in which they are aligned. When so operated while the machine is running, time lost to shutdown is avoided. This design, in effect, provides multiple valve ports enabling the machine periodically to extrude bone chips collected in the slots. A potential disadvantage of the multiple slots of the '647 patent is that if any slots are packed tightly with bone chips, there may be loss of easily flowable red meat through some slots while the remaining slots remain tightly packed. Ideally, all of the slots should be equally packed, should have equal pressure applied thereto during purging, and all extrude their waste material simultaneously. The likelihood of this happening can be expected to be slim, and any tightly packed slots may never be freed of unwanted materials until the machine is shut down and manually cleaned. Obviously, if a single one of the slots opens up and extrudes whatever bones have collected therein before any other slots can open, the soft, easily flowable meat immediately therebehind will continue flowing out until the valve is closed.
At this early stage of development of this art, little factual information exists as to the actual amount of valuable meat which is extruded with the unwanted bone, cartilage and gristle. Because of its high cost, the loss of red meat must be kept to an absolute minimum. It is doubted that any of the prior art bone chip removal systems has the capability of the system about to be described, in terms of efficient waste material removal with minimum loss of meat with the waste.